A teat cup forms a part of a milking machine, which part is attached to a teat of an animal to be milked. Traditionally a teat cup comprises a resilient liner and a teat cup shell. The teat to be milked is placed in the liner at one end of the liner, and a vacuum is applied to an opposite end of the liner. The teat cup shell is arranged around a portion of the liner. Between the teat cup shell and the liner a pulsation chamber is formed. The pulsation chamber is alternately connected to a vacuum source and to atmospheric pressure.
Teat cups of a more complex construction are also known. For instance, WO 2013/095290 discloses such a teat cup comprising a connector and a cartridge. The cartridge comprises a sleeve, having a first end and a second end, and a teat cup liner mounted in the sleeve and having an inner space for receiving a teat. A pulsation chamber is formed in the cartridge. The connector is configured to connect a milk conduit to the cartridge.
In an arrangement for automatically milking animals, sometimes called a milking robot, teat cups are automatically attached to the teats of an animal to be milked. Commonly a robot arm of the arrangement handles the teat cups.
WO 2005/122753 discloses a gripper device mountable on a robot arm of a milking robot provided for automatically attaching teat cups to the teats of a milking animal. The gripper device comprises an electromagnet for gripping teat cups made of a magnetic material. The electromagnet includes a coil feedable with a current, a core of a magnetic material arranged at least partly within the coil, and a support structure for holding the electromagnet. The core comprises two end portions in a single face of the electromagnet, wherein the two end portions constitute different poles of the electromagnet, and are shaped to be engagable with a teat cup in a close fit.
In an arrangement for automatically milking animals comprising an electromagnetic device for handling a teat cup, such as the above mentioned gripper device, the holding force between the electromagnetic device and a relevant teat cup sets a limit for the movements to be performed by the robot arm when handling the teat cup. Due to the inertia of the teat cup and the flexible milk tube attached thereto, sudden directional changes of the robot arm may cause the electromagnetic device to lose the teat cup. Moreover, an animal being milked may accidentally knock the teat cup out of the electromagnetic device.